The present invention is directed to a method, and material for use therewith, in the sanitizing of water, particularly for utilization in swimming pool sanitation, and the invention therefore will be described in connection therewith.
The popularity of swimming and swimming pools has been constantly increasing from year to year and is recognized as one of the best forms of exercise and recreation. However, swimming, more than any other recreational activity exposes the participants to unhealthy conditions, primarily because of the use of the same water by relatively large numbers of people. It will be appreciated that even a clean looking pool, filled with clear water, may be unsafe because of invisible infectious bacterial or other germs in the water.
Contaminants normally are constantly introduced into pool water from various sources, the air, rain, and the bathers. Probably the greatest quantity of harmful contaminants are introduced by the swimmers, which contaminants must be rapidly destroyed or removed from the pool. Those such as bacteria, viruses and algae, are destroyed by disinfectants and algaecides. Others, such as suspended matter, are removed from the pool water by passage of the water through a suitable filter. With the constantly increasing numbers of swimmers using common pool water, scientific water treatment and control is an absolute necessity for the protection of the participants. The term "pool water control" is a term applied to the treatment of pool water with chemicals to keep it sanitized, comfortable, healthful and visibly appealing.
An ideal disinfectant for such purposes would be one having a highly germicidal action, readily soluble in water, stable, non-toxic, non-corrosive to metals and non-irritating to the skin. Likewise, it should be capable of penetrating without being inactivated by organic materials, and must be of low cost.
All of the halogens are bactericidal and virucidal with fluorine possessing the greatest germicidal activity, followed by iodine, bromine and chlorine. However, because of its availability and economy, chlorine is used extensively for the large scale disinfection of water, swimming pools and food processing plants. Due to the constant contamination, sanitizing chemicals must be added regularly to swimming pool water to kill bacteria and control algae. Bacteria enter the pool through dust, rain and the human body, with the latter being the most significant source. These organisms may survive for weeks at temperatures near 70.degree. F. or for months at lower temperatures. The chlorine is added to the pool water, first to kill bacteria and algae, and secondly to oxidize undesirable organic matter, and in general a properly maintained chlorine residual in the pool water will generally accomplish the desired purposes.
The effectiveness of the sanitizing operation is also dependent upon the condition of the water as to its acidity or alkalinity, i.e. the pH, of the water, and proper balance thereof is important with respect to its effects on coagulation-filtration treatments, disinfecting effect of the chlorine, and physical effects on the swimmers, as for example, with respect to the eyes and skin.
As a result of studies, the recommended pH for pool water is from 7.2 to 7.6 and thus slightly on the alkaline side, preferably about 7.2, 7.0 being neutral, below 7.0 acidic, and above 7.0 alkaline. Generally, a pH below 7.0, or a very high pH, may result in skin or eye irritations while efficiency will be reduced below or above the optimum figures referred to, with maximum bactericidal efficiency of the chlorine residual being at a maximum between 7.2 and 7.6 which also is a non-irritating range.
As chlorine in water is a very active chemical agent, if a small amount is added thereto, it will react with the many substances dissolved or suspended in the water and will then be destroyed as a disinfecting agent. Chlorine readily reacts with reducing compounds such as hydrogen sulfide, manganese, iron and nitrites, and results in a loss disinfection. If enough chlorine is added to complete the reaction with the reducing compounds, then a little additional chlorine will react with any organic matter to form chlororganic compounds, which likewise have little or no disinfecting action, and may produce undesirable taste and odors. If enough chlorine is added to react with all the reducing compounds and the organic matter, a little additional chlorine will react with any ammonia which may be present to produce chloramines, which are weak disinfectants and which would require high concentrations and long contact times if effective destruction of bacteria were to be accomplished. When all the above reactions have been completed any additional chlorine added will be present as free, available chlorine residual, a very active disinfecting agent. The resulting graphic curve of these reactions of chlorine and water is termed the "chlorine demand curve".
To facilitate an understanding of the present invention it is believed that a brief review of the disinfecting action of chlorine likewise is desirable.
When chlorine, Cl.sub.2, dissolves in water, it immediately hydrolyzes according to the reaction: EQU Cl.sub.2 + H.sub.2 O .revreaction. HOCl + HCl
The chlorine of the hydrochloric acid does not contribute to the purification reaction. It is the hypochlorous acid, HOCl which actually kills the microbial bodies. The bactericidal power of hypochlorous acid is attributed to its ability to defuse through cell walls and reach the vital parts of the bacteria cells. Consequently, whether chlorine is added to water by chlorination or hypochlorination, the chemical action for sanitation and purification is the same, i.e. hypochlorous acid, HOCl.
Hypochlorous acid, being a weak acid, ionizes in water according to the equation: EQU HOCl .revreaction. H.sup.+ + OCl.sup.-
This equilibrium is instantaneous and reversible. However, when the pH is lowered, i.e. more acid or H.sup.+ ion is added to the system, the equilibrium is forced to the left and more hypochlorous acid is present. Conversely, when the pH is raised, the acid concentration, H.sup.+ ion is lowered and more of the hypochlorous acid is forced over toward the hypochlorite OCl.sup.-. Consequently, any free chlorine or hypochlorite added to water will immediately distribute itself into HOCl and OCl.sup.-, with the ratio for the two being controlled entirely by the pH value of the water. Obviously, in view of the great difference in killing power between the two, the pH value becomes of the greatest importance with respect to disinfection. At the recommended pH of 7.2 to 7.4, the HOCl, H.sup.+ and OCl.sup.- are in a suitable balance. In this connection, it should be noted that the pH value involved is that reached after the addition of the chlorine compounds, not the original pH value of the water.
Ideal swimming pool conditions will exist only if the right amounts of chemicals are added in balance, too little chlorine permitting live bacteria, and too much causing irritation to the eyes and mucous membranes.